The disclosure relates to a mobile working machine, for example an excavator, a truck with an attachment or an agricultural or forestry implement, having at least one working arm. Working arms of such working machines can also have a plurality of segments which are connected to one another in an articulated fashion, wherein a first end of the working arm is arranged in an articulated fashion on a superstructure of the working machine, and a second end of the working arm has a tool such as a shovel, a gripper or a hammer.
Often, the current position and attitude of the working arm, and in particular of the tool as well, are displayed to the operator of such a working machine as an operating point on a display, allowing the operator to work according to precisely predefined plans and providing direct feedback about attained heights, lengths, depths or angles of inclination of, for example, a moved about bulk material or soil or of the underlying surface which is to be formed or is already formed, in relation to the operating point of the working arm.
Such operator control displays are known, for example, from DE 201 16 666 U1 and from U.S. Pat. No. 5,854,988 A.
In this context, the operating point and the attitude of the tool are also determined by inclination sensors because of the possibility of easy retrofitting, wherein at least a first inclination sensor is arranged on the superstructure and a second inclination sensor is arranged on the working arm. The position and attitude of the tool and/or the operating point can be calculated from the angles of inclination of the working arm and superstructure.
However, since the inclination sensors used are sensors which are based on the principle of measuring inertia such as, for example, gravitation-sensitive pendulums, they are also sensitive to accelerations owing to shocks and vibrations such as unavoidably occur when such working machines are in use. In particular, measurement errors occur when the attached tool is accelerated and braked. Such movement-induced accelerations can considerably disrupt the measurement of the operating point of the tool or make it impossible at certain times.
Nevertheless, when the tool is in a stationary state, precise reference values for calculating the actual value of an operating point at the start and at the end of a change in the operating point can be determined by the inclination sensors accompanied by evaluation in a central control unit. However, inclination sensors are unsuitable for controlling the operating point in order to track and control changes in the position or in the operating point of the tool since they provide precise measurement values of the inclinations only when the working machine is in a stationary state.
From other technical fields it is known to use acceleration-based inclination sensors and rotational speed sensors in order to control the position of a robot, of a missile or of a vehicle. Document WO 01/57474 A1 discloses such a method in which a quaternion representation is used to calculate an operating point. Such systems are highly complex and associated with high costs.
The object of the disclosure is to specify a mobile working machine with a device for detecting the position and controlling the operating point for implements, which device permits an operating point to be automatically moved with a small number of easy-to-integrate components. A further object of the disclosure is to specify a method for such an operating point control system.
According to the disclosure, this object is achieved. Advantageous developments of the disclosure are described herein.
A mobile working machine according to the disclosure has a working arm which is arranged in an articulated fashion with a first end on a superstructure of the working machine. A tool is arranged at a second end of the working arm so as to be capable of moving to an operating point. At least one first inclination sensor is arranged on the superstructure, and at least one second inclination sensor is arranged on the working arm. Furthermore, at least one hydraulic cylinder is provided which is arranged in an articulated fashion between the superstructure and the working arm in order to change the position of the operating point. Furthermore, a control unit is provided for processing signals of the at least two inclination sensors for determining an operating point as a reference operating point and for determining a change in position of the operating point by calculating a cylinder travel on the basis of a volume flow into or out of the hydraulic cylinder.
This mobile working machine has the advantage that it can be implemented with simple control and measuring components by monitoring the actual position before a change in position as a reference position and during the change in position by means of a cylinder travel distance, wherein the change in the cylinder travel permits a new actual position which can be checked by a precise position when the working arm is in a stationary state, and the difference with respect to a setpoint value can be compensated by feeding back the precisely measured actual position into the control unit via a feedback branch the difference between the actual position and the setpoint position.
As a result, all that is necessary is to provide at least two inclination sensors for the control device. The necessary cylinder travel for a change in position can, on the other hand, be determined by the known volume flow and the known cylinder dimensions by measuring the time or predefining the time. As a result, an economical solution for the monitoring and control of the changes in position of the working arm of a working machine is achieved. The implementation of the detection of a position for the implements of a mobile working machine with a small number of simple components which can be integrated is therefore possible and as a result of the possibility, now provided, of automatically moving to operating positions, the performance factor of the mobile working machine is advantageously improved.
In a further embodiment of the disclosure, the working arm has a number of segments which are connected to one another in an articulated fashion. In this context, each of these segments is equipped with an additional hydraulic cylinder in order to move said segment with respect to the other segments of the working arm. Each of the segments of the working arm then requires an additional inclination sensor to determine the reference point, and for the change in position of such a segment it is in turn possible to use the cylinder travel which can be calculated by means of the volume flow in the corresponding additional hydraulic cylinders.
If the superstructure is rigidly connected to a chassis, as in the case in a tractor, the operating point of the tool relative to the tractor can be determined with the components according to the disclosure. However, in the case of excavators, the superstructure is mounted so as to be horizontally rotatable with respect to the chassis, with the result that in a further embodiment of the disclosure a means of sensing the rotational angle in order to determine the operating point is additionally provided. This sensing of the rotational angle of the superstructure with respect to the chassis now advantageously permits the operating point, and the change in position thereof, to be spatially sensed in a three-dimensional coordinate system.
The inclination sensors, which can sense the reference working point of the mobile working machine precisely in a starting position of rest and also senses the actual position of a change in position by the hydraulic cylinder, preferably have pendulum bodies, refractive liquid levels, micromechanical or conductormetric or capacitively acting structures. In this context, excavators, tractors with front loaders, telescopic loaders, backhoe loaders, wheel loaders, forestry machines, communal working machines, agricultural machines and/or loading cranes are provided as mobile working machines.
A method for controlling the operating point of a working arm of a mobile working machine has the following method steps. Firstly, angles of inclination of the superstructure and of a working arm which is arranged in an articulated fashion with a first end on the superstructure are measured by means of inclination sensors. Then, a first reference position of the operating point at a second end, bearing a tool, of the working arm is calculated taking into account the measurement results of the measured angles of inclination. Finally, a change in position of the operating point into a predefined setpoint position is carried out by means of a hydraulic volume flow during a limited time interval. The change in position is subsequently checked by the inclination sensors by determining an actual position of the operating point. By comparing the actual position with the predefined setpoint position into which the working arm is to be pivoted, a difference is obtained in the form of a control deviation between the setpoint position and the actual position, which subsequently leads to a reduction in a difference between a setpoint position and the actual position by repeatedly running through the first four method steps.
This method has the advantage that a small number of iterative steps make it possible to ensure that the actual position virtually reaches the setpoint position without complex calculations or complex structures or complex measuring techniques being necessary to reach a predetermined, changed operating point precisely. In this context, the known volume flow, the effective piston area and the time period are taken into account for the calculation of the change in position of the operating point. From the travel which is to be executed for a change in position, the oil flow and the activation duration can be calculated and the working machine is correspondingly controlled in order, for example, to permit operating points to be moved to automatically. First results show that with the method according to the disclosure it is possible to achieve a high degree of positional accuracy of the changed operating point. The deviations between the actual position and the setpoint position can finally be reduced by iterative steps.
Furthermore, it is possible to sense safety positions for the operating points and to store critical operating points by means of a teaching method, which operating points are then no longer overshot by the mobile working machine with a working arm. It is furthermore possible to sense constant changes in position and to store by means of a teaching method in such a way that subsequent control does not become necessary.
In all these method variants it is, however, important that the measurement of the respective reference position and of the actual position is carried out by means of the inclination sensors in a position of rest of the mobile working machine and of the working arm.